Ten asymptomatic patients with NIDDM received either a single oral dose of MK-912 (2 mg) or placebo in a double-blind, cross-over study. The b-cell function was measured by the acute insulin response (AIR) to glucose (1.66 mmol/kg intravenously [IV]) and by the AIR to arginine (5 g IV) during a hyperglycemic glucose clamp at a mean glucose level of 32.1 mmol/L to provide an estimation of maximal B-cell secretory capacity. A-cell function was estimated by the acute glucagon response (AGR) to arginine during the glucose clamp. Alpha 2-adrenergic blockade was achieved, as there were substantial increases in plasma norepinephrine after treatment with MK-912 but not placebo. MK-912 caused a significant although a modest decrease of fasting plasma glucose (FPG) that was associated with a small increase of fasting plasma insulin, C-peptide, and glucagon. MK-912 tended to increase the AIR and the C-peptide response to glucose.

Proximal tubule cells were isolated from Sprague-Dawley rats and processed to extract membranes into TM buffer. Membranes were incubated at 25 deg-C in a 400 micro-L final volume of TM buffer containing the 3H-labeled MK-912. After 45 minutes membrane-bound radioactivity was separated from free by rapid filtration. Retained radioactivity was counted by liquid scintillation spectrometry. The difference between total and nonspecific binding determined in the presence of 10^5 M phentolamine. For saturation experiments, the final concentration of MK-912 ranged from 0.25 to 8 nM. The maximal binding and Kd were determined to be 118 fmol/mg protein, and 1.65 nM, respectively.